Advances in weapon systems have resulted in soldiers carrying additional gear to enhance combat effectiveness, but at the cost of increased weight. Today soldiers on combat patrols in Afghanistan typically carry 92 to 105 pounds of mission-essential equipment which includes extra ammunition, chemical protective gear and cold-weather clothing. The overload causes fatigue, heat stress, injury, and performance degradation for soldiers. To ensure that America's soldiers maintain their overwhelming combat edge into the 21 st century, making the load lighter for soldiers has moved to the top of the priority list in the Army.
Despite years of research and development, the Army's weapons and equipment is still too heavy to allow foot soldiers to maneuver safely under fire. One of the heaviest pieces of load for soldiers is the ammunition. Every solider has to carry a lot of ammunition during combat. For example, the weight of 0.50 caliber ammunition is about 60 pounds per box (200 cartridges plus links). It is burdensome for a soldier to move around with heavy ammunition aside from carrying additional gear at the same time. Conventional ammunition cartridge cases for rifles and machine guns, as well as larger caliber weapons, are usually made from brass, which is heavy, expensive, and potentially hazardous. There exists a need for an affordable lighter weight replacement for brass ammunition cartridge cases that can increase mission performance and operational capabilities.
As early as 1960, the U.S. military has recognized the benefits of using polymer or polymer composite materials for cartridge case applications, and since then much research has been carried out by the military and ammunition industry, The previous studies have demonstrated feasibility but have not achieved consistent and reliable ballistic results. Recent efforts have focused on a two-piece metal and plastic hybrid cartridge case design which encountered numerous failures. On the civilian side, the development effort focused on low-pressure and low muzzle-speed cartridge case applications.
Lightweight polymer cartridge casing ammunition must meet the reliability and performance standards of existing fielded ammunition and be interchangeable with brass cartridge casing ammunition in existing weaponry. At the same time, the light-weight polymer cartridge casing ammunition must be capable of surviving the physical and natural environment to which it will be exposed during the ammunition's intended life cycle. In addition, the polymeric cartridge casings should require little to no modification of conventional ammunition manufacturing equipment and methods.
To date, polymeric cartridge casings have failed to provide satisfactory ammunition with sufficient safety, ballistic and handling characteristics. Most plastic materials, however, even with a high glass fiber loading, have much lower tensile strength and modulus than brass. Existing polymer/composite casing technologies as a result have many shortcomings, such as insufficient ballistic performance, cracks on the case mouth, neck, body and/or base, bonding failure of metal-plastic hybrid cases, difficult extraction from the chamber, incompatibility with propellant (particularly for double base propellants), insufficient high temperature resistance (burn holes) and chamber constraints produced by thicker case walls.
Other shortcomings include the possibility of the projectile being pushed into the cartridge casing, the bullet pull being too light such that the bullet can fall out, the bullet pull being too insufficient to create sufficient chamber pressure, the bullet pull not being uniform from round to round, and portions of the cartridge casing breaking off upon firing causing weapon jam or damage or danger when subsequent rounds are fired or when the casing portions themselves become projectiles.
To overcome the above shortcomings, improvements in cartridge case design and performance polymer materials are needed.